The present invention relates to a laser processing device and laser processing method whereby laser processing such as processing for the formation of minute holes is performed on an article to be processed which is in the form of a sheet, such as a circuit board, using a laser beam.
FIG. 1 shows the construction of a holding device for an article to be processed which is in the form of a sheet in a prior art laser processing device. This laser processing device 130 is constructed so as to perform laser processing by holding a sheet-like article 131 to be processed at a prescribed position.
In FIG. 1, through-holes 134a are provided on a suction plate 134 arranged on a holding base 133. The sheet-like article 131 to be processed placed on suction plate 134 is held in a prescribed position by suction created by vacuum evacuation from vacuum evacuation port 135. Processing to produce a minute hole is achieved by directing a laser beam on to article 131 held in this prescribed position.
FIG. 2 shows another known CO.sub.2 laser processing device for processing the surface of an article in the form of a thin sheet consisting of a metal sheet or the like at high speed and high accuracy, in which the article is located in position and a laser beam is directed on to the surface of this article. In such a laser processing device, as shown in FIG. 2, the undersurface of article 41 to be processed is supported at a large number of locations by spikes 42, leveling being achieved by utilizing the weight of this article 41 and processing being performed by directing a laser beam 43 on to article 41 from its upper surface.
However, in the prior art example shown in FIG. 1, when hole-forming processing of article 131 is performed by a laser beam, laser light passing through article 131 by means of the holes that are thus formed is reflected by suction plate 134 and this reflected light heats up and deforms article 131 to be processed. Since circuit board materials etc. are easily deformed by heat, through-holes for preventing reflection are provided, as a counter-measure, beforehand in suction plate 134 at positions corresponding to the positions in which the holes are to be formed in article 131. However, since the position of such anti-reflection through-holes is different depending on the type of article 131 to be processed, it is difficult to make these correspond with a large number of product types. Although it is possible to cope with changes in the position in which processing is effected if the antireflection through-holes are formed large enough, if article 131 to be processed is thin, distortion is produced by the suction, lowering processing accuracy. Also, since article 131 to be processed is fixed in position by vacuum suction, the residue produced by processing is removed by this suction, but there was the problem of blockages being produced by this residue in parts of the suction flow path.
Further, the prior art example shown in FIG. 2 which is employed for forming through-holes by laser processing for via electrodes in the thin resin sheet or metal sheet for multi-layer circuit boards was subject to the following problems. Specifically, thin sheet such as resin sheet has poor shape stability and is liable to curl so if this prior art method is applied to such thin sheet, large undulations are left in the vicinity of the center of the thin sheet. This gives rise to the problem that such changes in surface height may exceed the allowed range of working distance of the laser beam, making accurate processing impossible.